Heart attacks are a common cause of death. A heart attack occurs when a portion of the heart tissue loses circulation and, as a result, becomes damaged (e.g., because of blockage in the heart vasculature). Heart attacks and other abnormalities can lead to ventricular fibrillation (VF), which is an abnormal heart rhythm (arrhythmia) that causes the heart to lose pumping capacity. If such a problem is not corrected quickly—typically within minutes—the rest of the body loses oxygen and the person dies. Therefore, prompt care of a person undergoing ventricular fibrillation can be key to a positive outcome for such a person.
One common way to treat ventricular fibrillation is through the use of an electrical defibrillator that delivers a relatively high voltage shock to the heart in order to restore a healthy and regular, rhythm associated with strong myocardial contractility. People who have had previous problems with ventricular fibrillation can be implanted with an automatic defibrillator that constantly monitors the condition of their heart and applies a shock when necessary. Other such people can be provided with a wearable defibrillator in the form of a vest such as the LIFEVEST product from ZOLL Medical Corporation. Other people can be treated using an external defibrillator, such as in a hospital or via an automatic external defibrillator (AED) of the kind that is frequently seen in airports, public gymnasiums, and other public spaces. Defibrillation can be delivered in coordination with cardiopulmonary resuscitation, which centers on the provision of repeated compressions to a victim's chest. For example, a rescuer can press downward repeatedly with the palms of the hands, or via a mechanical compression device such as the AUTOPULSE non-invasive cardiac support pump from ZOLL Medical Corporation.
People undergoing ventricular fibrillation can be more receptive to a defibrillating shock in some instances compared to others. For example, research has determined that an indication of whether a shock that is delivered would likely result in successful defibrillation can be obtained using a computation of amplitude spectrum area (AMSA), or other computational methods that use either time-based or spectrum-based analytic methods to calculate, from an electrocardiogram (ECG), a prediction of defibrillation shock success.